1. Field of the Invention
The present invention generally relates to a semiconductor accelerometer. More particularly, the present invention relates to a semiconductor accelerometer in which an accelerometer chip is housed within a casing.
2. Description of the Related Arts
Conventional accelerometers can be classified into piezo type, electrostatic capacity type and metal strain type by the method of converting acceleration into electric signals. Irrespective of these types, however, the structure thereof is commonly composed of a proof mass and a plurality of beams to suspend the proof mass. In general reference to the structure of a beam, the thicker the beam part is, the higher the static fracture strength, but the lower the sensitivity is; reversely, the thinner the beam part is, the higher the sensitivity is, but the lower the static fracture strength is. This indicates the difficulty in having high the sensitivity and at the same time high static fracture strength. In order to achieve a desired level of sensitivity, therefore, the static fracture strength has to be sacrificed, and in order to compensate for the sacrificed static fracture strength, some countermeasures have to be taken, such as filling the casing with some viscous liquid, providing some stopper material to prevent excessive deformation of the beam and providing some buffer material to the outer periphery of the casing to prevent the transmission of impacts to the beam (as disclosed in the Japanese Patent Unexamined Publication Nos. 64-59075, 3-107769 and 63-206663 and the U.S. Pat. No. 5,060,504).
However, as these countermeasures require contrivances to provide some viscous liquid or some beam stopper material, the materialization of a semiconductor accelerometer which does not require any viscous liquid or any beam stopper material has been awaited.